fix: resolve chat prompt read-only state for subagent sessions

Allows prompting subagent sessions without needing the parent record
Keeps subagents read-only when prompting is disabled
Covers root and subagent cases with unit tests

packages/ui/src/components/chat/ChatContainer.tsx

@@ -43,6 +43,7 @@ import {
     useScopedBlockingPermissions,
     useScopedBlockingQuestions,
     useParentSession,
+    useSession,
 } from '@/sync/sync-context';
 import { useSync } from '@/sync/use-sync';
 import { usePlanDetection } from '@/hooks/usePlanDetection';
@@ -53,6 +54,7 @@ import { getEmbeddedSessionChatOriginSessionId } from '@/components/layout/conte
 import { isFullySyntheticMessage } from '@/lib/messages/synthetic';
 import { normalizeUserDisplayParts } from './message/normalizeUserDisplayParts';
 import { findShellCommandForMessage, isUserShellMarkerMessage } from './lib/shellBridge';
+import { resolveChatPromptReadOnly } from './chatPromptReadOnly';
 
 const EMPTY_MESSAGES: Array<{ info: Message; parts: Part[] }> = [];
 const IDLE_SESSION_STATUS = { type: 'idle' as const };
@@ -679,6 +681,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ active = true, aut
     const isDesktopExpandedInput = isExpandedInput;
     const useCompactDraftLayout = isMobile || isVSCode || chatSurfaceMode === 'mini-chat';
     const messageListRef = React.useRef<MessageListHandle | null>(null);
+    const currentSession = useSession(currentSessionId, effectiveSessionDirectory);
     const parentSession = useParentSession(currentSessionId, effectiveSessionDirectory);
 
     // In the embedded session-chat iframe, hide "Return to parent" when
@@ -712,7 +715,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ active = true, aut
             {t('chat.container.returnToParent.label')}
         </Button>
     ) : null;
-    const promptReadOnly = parentSession ? !allowPromptingSubagentSessions : readOnly;
+    const promptReadOnly = resolveChatPromptReadOnly(currentSession, allowPromptingSubagentSessions, readOnly);
 
     React.useEffect(() => {
         // VS Code/Cursor/Positron webviews delete window.parent (and window.top).

packages/ui/src/components/chat/chatPromptReadOnly.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, test } from 'bun:test';
+import type { Session } from '@opencode-ai/sdk/v2';
+
+import { resolveChatPromptReadOnly } from './chatPromptReadOnly';
+
+const session = (parentID?: string): Session => ({
+    id: 'session',
+    slug: 'session',
+    title: 'Session',
+    version: '1',
+    projectID: 'project',
+    directory: '/repo',
+    parentID,
+    time: { created: 1, updated: 1 },
+});
+
+describe('resolveChatPromptReadOnly', () => {
+    test('allows prompting a subagent without requiring its parent record', () => {
+        expect(resolveChatPromptReadOnly(session('parent'), true, true)).toBe(false);
+    });
+
+    test('keeps a subagent read-only when prompting is disabled', () => {
+        expect(resolveChatPromptReadOnly(session('parent'), false, false)).toBe(true);
+    });
+
+    test('preserves the surface read-only state for root sessions', () => {
+        expect(resolveChatPromptReadOnly(session(), true, true)).toBe(true);
+        expect(resolveChatPromptReadOnly(session(), true, false)).toBe(false);
+    });
+});

packages/ui/src/components/chat/chatPromptReadOnly.ts

@@ -0,0 +1,13 @@
+import type { Session } from '@opencode-ai/sdk/v2';
+
+export const resolveChatPromptReadOnly = (
+    session: Session | null | undefined,
+    allowPromptingSubagentSessions: boolean,
+    readOnly: boolean,
+): boolean => {
+    if (session?.parentID) {
+        return !allowPromptingSubagentSessions;
+    }
+
+    return readOnly;
+};